Joints are common components in today's automotive vehicles. Typically, joints are used for transmission of a rotating motion. When transmission of a rotating motion is desired at a generally constant velocity a constant velocity joint (CVJ) is utilized. Various styles of constant velocity joints are common and include ball-type fixed joints, tripod fixed joints, plunging ball joints, and the like. The various styles of joints are currently used in front-wheel drive vehicles, rear-wheel drive vehicles and on propeller shafts (propshafts) found in rear-wheel drive, all-wheel drive and four-wheel drive vehicles. The constant velocity joints are generally grease lubricated for life and sealed by a sealing system when used on propshafts. Therefore, constant velocity joints are sealed in order to retain grease inside the joint while keeping contaminants and foreign matter, such as dirt, water, and the like out of the joint. To achieve this protection the constant velocity joint usually includes a sealing system. The CVJ is usually enclosed at an open end of an outer race by a sealing boot and boot cover made of a rubber, thermoplastic, silicone type material, and the like. The opposite end of the outer race is generally enclosed by a dome or cap, commonly known as a grease cap. A monoblock or integral stem and race style joint is sealed at the opposite end by the internal geometry of the outer race. This sealing and protection of the constant velocity joint is necessary because contamination of the inner chamber of the joint generally will cause internal damage and destruction of the joint. Furthermore, once the inner chamber of the joint is partially filled and thus lubricated, it is generally lubricated for life.
A main function of a CVJ is the transmission of rotational forces. During operation, the constant velocity joint transmits torque. The torque transfer generates heat by the internal friction of the joint along with other transmission inefficiencies. Generally, as the speed and torque increase, the heat generation of the constant velocity joint also increases. A further effect of increased speeds is that the velocity of the grease increases because the internal action of the joint acts like a pump to causes the grease to be pumped out of the joint and into the sealing system. This phenomenon increases pressure on the sealing system. The high internal temperatures in the constant velocity joint also affect the lubricant grease, which is in contact with the sealing system. With higher temperatures the boot and boot cover of the sealing system become more vulnerable to cracking and rupture and the durability of the constant velocity joint that is generally sealed for life is reduced. Furthermore, heat that is generated within the sealing system is transferred to the outer race of the CVJ. As a result, premature cracks, ruptures and blowouts of the sealing system further reduce the life of the boot. With the heat affecting the life and material of the sealing system, the boot and boot cover are also more vulnerable to external damage due to strikes or blows by contaminants from the environment of the automotive vehicle. These contaminants can be anything from rocks, mud, road debris, or any other object capable of being thrown by the tires or deflected into the boot or boot cover of the sealing system of the constant velocity joint. These contaminants striking the boot will further reduce the sealability of the boot and boot cover while increasing the possibility of ruptures, blowouts, and the like. Accordingly, life of the constant velocity joint is ultimately reduced.
Therefore, there is a need in the art for a joint having a sealing system that is protected from contact with foreign objects found in the outside environment of the joint. The ability to protect the sealing system from external objects will reduce early deterioration of the boot and boot cover that may result in eventual failure of the sealing system and ultimate failure of the joint.